In the prior art, the threaded rod device for shaping a nylon zipper is formed by two parallel threaded rods for winding nylon wires into nylon gripper elements. With reference to FIG. 1, a center wire 1 enters into a shaping mold 4 from a center of a clip 3. The nylon wire 2 wound the central wire 1 is guided into the shaping mold from a lateral side. When the wires 1 and 2 have entered into the shaping mold 4, two threaded rods 5 in the shaping mold will clamp the nylon wires into elliptical shape. Then one end of the nylon gripper element is beaten into a nose portion 71 by transversally moving a beating head 6. Thereby, a nylon gripper element is formed.
After forming the nylon gripper element 7, the seaming wire 8 of the zipper is seamed to a cross strip 9, as shown in FIG. 2. The two banks of gripper elements 7 are engaged by the nose portions 71 thereof.
When the seaming wire 8 exposes from the nylon gripper elements 7 and a pull head of the zipper is pulled, the inner wall will rubber the exposed seaming wire 8. Thereby, when the pull head slides, a resisting force generates. Moreover, after long using time, the seaming wire will break. Further, the seaming wire 8 easily slides on the fastener structure, especially, when lateral or twisting force applies upon the seaming wire 8. The seaming wire 8 laterally exposes from the nylon gripper elements. If the zipper is large, the exposing of the seaming wire 8 is more apparent. Since the seaming wire 8 easily slides on the nylon gripper elements, the pull resisting force of the nylon gripper elements for preventing the pull force at two sides of the zipper is low.